The pressure at which typical gas distribution systems supply gas may vary according to the demands placed on the system, the climate, the source of supply, and/or other factors. However, most end-user facilities equipped with gas appliances such as furnaces, ovens, etc., require the gas to be delivered in accordance with a predetermined pressure, and at or below a maximum capacity of the end-user appliance. Therefore, process fluid regulators are implemented in these distribution systems in order to ensure that the delivered gas meets the requirements of the end-user facilities.
Process fluid regulators typically employed in such gas distribution systems are generally well known in the art. FIG. 1 shows a common process fluid regulator 10. The fluid regulator includes a regulator body 12, a control element 14, and an actuator 16. The regulator body 12 defines a fluid flow path 18 extending from a fluid inlet 20 to a fluid outlet 22 and through an orifice 24 operatively disposed between the fluid inlet 20 and the fluid outlet 22. The control element 14, such as a valve disk or plug, shifts to regulate the flow of fluid along the fluid flow path 18 through the orifice 24. The actuator 16 is operatively connected to the regulator body 12 to control the position of the control element 14 relative to the orifice 24. The actuator includes a housing 26, a diaphragm 28 disposed inside the housing 26, and a linkage operatively connecting the diaphragm 28 to the control element 14. The diaphragm 28 separates the housing 26 into a first chamber 30 hydraulically connected to the fluid outlet and a second chamber 31 hydraulically connected to the atmosphere. The linkage includes a lever 32 having a first end operatively connected to the diaphragm 28 and a second end operatively connected to a valve stem 34 operatively connected to the control element 14. Movement of the diaphragm 28 in response to pressure changes at the outlet 22 causes the linkage to shift the control element 14 in a manner to maintain a the process fluid pressure within a preselected range at the fluid outlet 22.
The actuator 16 includes a single control spring 36 that is operatively connected to the diaphragm 28. The spring 36 is arranged to bias the diaphragm 28 against the fluid pressure with a selected force so as to maintain the preselected pressure range at the fluid outlet 22. Typically, the force exerted by the control spring 36 can be adjusted with an adjusting screw 38. Adjustment of the adjusting screw 38 results in adjustment in the preselected range maintained at the outlet 22. This arrangement, with the single control spring 36, has an advantage of being simple to assemble and maintain and has been used extensively for many years. However, use of the single control spring 36 can inherently be prone to stability limitations at certain resonant frequencies, which may contribute to undesirable valve flutter under some operating conditions.